RU2181408C1 - Method for soil stabilization - Google Patents

Abstract

FIELD: construction, applicable for stabilization of clayey, loamy, sandy and loess soils, especially when steel constructions subjected to acid corrosion are available in the soils. SUBSTANCE: the method is accomplished as follows. First 4-2-percent aqueous solution of alkali, for example, sodium hydroxide, is introduced in the soil, then 5-3-percent aqueous solution of magnesium chloride is introduced. EFFECT: prevented acid corrosion of steel constructions being in the stabilized soil, reduced cost of the stabilization performed.

Description

 The invention relates to the construction and can be used for fixing clay, loamy, sandy, sandy loam and loess soils, especially in the case of steel structures in the soil susceptible to acid corrosion.

 A known method of electrochemical fixation of the soil by introducing a mixture of 5-8% aqueous solution of resocin and 10-15% aqueous solution of sulphate-distillery concentrate in a ratio of 1: 0.8-1.2 and in the second half of the period 15- 20% aqueous formaldehyde solution, and through the cathode-injector during the entire period of a 2-3% aqueous sodium dichromate solution; additional injection of a 15-20% aqueous formaldehyde solution is also carried out through a neutral injector installed at the same distance from the anode and cathode, see ed. St. SU 1020513, class E 02 D 3/12, 08.21.1981.

 The disadvantages of this method are the small penetration depth of the solutions due to the large size of the polymer particles contained in them, as well as the high cost of soluble materials.

 A known method of electrochemical fixation of the soil, including immersion in the soil of the electrodes, applying DC voltage to them, introducing a cementing silicate material with its treatment with carbon dioxide, see ed. St. SU 1099400, class E 02 D 3/11, 07/02/1982.

 The disadvantage of this method is also the small radius of penetration of the cementitious material, which is due to the large size of the anions of silicic acid, as well as the fact that the anions move towards the anode against water flow in the soil.

A known method of fixing the soil, which consists in the fact that two solutions are introduced into the soil in turn: sodium silicate and calcium chloride. Solutions are injected into the soil through injectors or wells, or by impregnation from above; it is also possible to introduce solutions into the soil using the electroosmotic method. As a result of a physico-chemical reaction between these solutions, a gel of silicic acid is formed. The reaction between the solutions occurs according to the scheme:
Na ₂ OHSiO ₂ + CaCl ₂ + mH ₂ O -> nSiO ₂ (m-1) H ₂ O + Ca (OH) ₂ + 2NaCl
the resulting gel of silicic acid determines the fixation of the soil (R _cm to 8.0 MPa), see A.I. Khalikulov et al. Chemistry in construction, Tashkent, 1983, p. 19).

 This technical solution is taken as a prototype of the present invention.

 Its disadvantage consists mainly in the short range (several tens of centimeters) of penetration of the cementing material, since the anions of silicic acid are large; In the electroosmotic method of introducing solutions, silicic acid anions move towards the anode against water flow in the soil. Therefore, this method (like any other associated with silicatization) is of little use for finely dispersed soils (clays, loams, etc.). In addition, sodium silicate (water glass) is an artificial material, which leads to a high cost of implementing the method.

 Also a significant disadvantage of the prototype is a significant change in the treated soil in comparison with the original (shrinkage).

 The present invention is based on the solution of the problem of creating an effective and relatively inexpensive method of fixing finely dispersed soil, in particular, in the presence of steel structures susceptible to acid corrosion, as well as a significant reduction in shrinkage of the processed soil.

 According to the invention, this problem is solved due to the fact that in the method of fixing the soil, which consists in alternately introducing into the soil two solutions, first a 4-20% aqueous solution of alkali, for example sodium hydroxide, is introduced, and then 5-30% aqueous magnesium chloride solution.

The following chemical reaction occurs:
NaOH + MgCl ₂ + H ₂ O -> xMgO • yH ₂ O • zMgCl ₂ + NaCl
It turns out a product cementing the soil and having a complex composition, characterized by variable values of x, y, z.

 The applicant has not identified technical solutions identical to the claimed invention, which allows us to conclude that it meets the criterion of "novelty."

 The proposed method has an important, fundamentally new property: cement-forming ions are small cations with high mobility in the soil. With the mechanical introduction of solutions into the soil with small pores, small-sized cations easily penetrate a large distance from the place of their introduction (injection, irrigation).

 With the electroosmotic introduction of solutions, cations move toward the cathode together with the water flow (and not against the flow), which facilitates their penetration over a large distance from the electrode. In addition, it should be emphasized that magnesium chloride (bischofite) is widespread in nature and very inexpensive, which greatly reduces the cost of implementing the method. The introduction of an alkali solution before the introduction of magnesium chloride prevents acid corrosion of steel structures in the ground. The volume of cultivated soil remains virtually unchanged.

 The applicant has not identified any sources of information containing information about the influence of the distinguishing features of the present invention on the achieved technical result, which determines, according to the applicant, the claimed technical solution meets the criterion of "inventive step".

 The essence of the proposed method is illustrated by the following examples (laboratory).

 Example 1. Loam is heavy, silty, tape, soft, fluid.

The porosity of the soil is 0.5;
natural humidity W - 0.394;
soil density ρ - 1.32 t / m ³ ;
volumetric humidity - 0.52;
filtration coefficient K _f - 2.0 • 10 ^-5 m / day;
angle of internal friction φ - 6 degrees;
soil compressive strength C - 0.05 kg / cm ² .

The soil sample was fixed with dimensions of 15 • 9 • 9 cm ³ using electroosmotic injection of solutions at an electric field strength of 1-2 V / cm.

Initially, a 4% aqueous NaOH solution was introduced in a volume of 270 ml. After a day, a 5% aqueous solution of MgCl ₂ was introduced in a volume of 330 ml. After 2 days, the electric current was turned off, while the soil continued to gain strength for another 3 days. Then, tests of the treated soil for strength were carried out. The following results were obtained:
C - 4.9 kg / cm ² ; φ - 22 deg.

 Example 2. Sandy soil.

Porosity - 0.3;
natural humidity W - 0.344;
soil density ρ - 1.53 t / m ³ ;
volumetric humidity - 0.53;
filtration coefficient K _f - 3.1 • 10 ^-4 m / day;
angle of internal friction φ - 7 degrees;
soil compressive strength C - 0.05 kg / cm ² .

The processing of a soil sample weighing 1860 g was carried out by sequential injection of a 20% aqueous solution of NaOH (170 g) and a 30% aqueous solution of MgCl ₂ (190 g). Solutions were administered directly one after another. Then within 3 days the soil gained strength. The following results were obtained:
C - 6.1 kg / cm ² ; φ - 25 deg.

 Example 3. Loam is light, dusty, layered, soft plastic.

The porosity of the soil is 0.4;
natural humidity W - 0.278;
soil density ρ - 1.52 t / m ³ ;
volumetric humidity - 0.42;
filtration coefficient K _f - 4.0 • 10 ^-5 m / day;
angle of internal friction φ - 9 degrees;
soil compressive strength C - 0.07 kg / cm ² .

Processing the soil sample with dimensions of 15 • 9 • 9 cm ³ was carried out using electroosmotic injection of solutions at an electric field strength of 1-2 V / cm.

First, a 10% aqueous NaOH solution was introduced in a volume of 110 ml. After a day, a 15% aqueous solution of MgCl ₂ was introduced in a volume of 110 ml. After 2 days, the electric current was turned off, the soil was gaining strength for another 3 days. The following results were obtained:
C - 5.1 kg / cm ² ; φ - 24 deg.

 The method is carried out using conventional equipment and available materials, which determines, according to the applicant, his compliance with the criterion of "industrial applicability".

Claims (1)

 The method of fixing the soil, which consists in the alternate introduction of two solutions into the soil, characterized in that a 4-20% aqueous solution of alkali, for example sodium hydroxide, is first introduced, and then a 5-30% aqueous solution of magnesium chloride is introduced.